It is well known that contaminants and corrosion products, such as tubercles, rust, scale and the like, can form inside metallic water mains and pipes as a result of corrosion, and can form layers, which can build up over time to form lumps and mounds, masking areas of internal metal loss.
These occlusive build ups can severely reduce the internal bore of pipes, leading to reduced flow capacity and a necessary increase in pumping pressure to maintain a sufficient supply of water or other fluid flowing through the pipe. Moreover, the build-up of corrosion products can adversely affect the quality of the fluid flowing in the pipe, creating problems such as “red water” in drinking water systems.
The use of abrasives in a flowing air or gas stream for pipe cleaning to remove the above-noted contaminants and corrosion products is well known. The generic process of “sandblasting” is a mature technology frequently used in larger-diameter, man-entry pipes for surface preparation, and the process of injecting garnet grit (beach-sand consistency) into a flowing compressed airstream has been used previously in small diameter pipes to facilitate the removal of corrosion products as well as the surface preparation of the internal pipe circumference for immediate, protective coating. In fact, the U.S. Navy used this process for numerous years to remove corrosion from the internal bore of small-diameter pipes installed on its aircraft carrier fleet, after which, the pipes were remotely coated with a protective epoxy. Recently, various combinations of gases and abrasives, such as the use of frozen gas pellets and different propellant gases, have been combined to attempt to remove contaminants and corrosion products, as well as to prepare surfaces of the internal pipe circumference for the later application of an immediate, protective coating or liner.
The process of abrasive blasting becomes more complex wherever pipeline entry is not possible by virtue of pipe diameter (too small) or location (inaccessible). The deployment of an abrasive from a single entry point, over medium/long pipe distances, requires a novel process. This process uses special equipment and produces a different surface blast pattern and outcome.
More recently, larger-sized abrasives (e.g. stones versus grit), in combination with larger air movers (compressors/blowers), have been used to clean corroded water pipes in diameter ranges of 4″ through 8″ in the UK. This process deploys an abrasive in a gas stream and was (again) used to remove heavy corrosion products in small diameter pipes and prepare the internal circumference for immediate protective coating.
However, these conventional systems do have drawbacks and limitations. For one thing, cleaning systems that deploy an abrasive in a gas stream, such as that described in United States Patent Application Publication No. 2009/270016 (Christopher), disclose the use of a pressurized hopper for dispensing the abrasive particulate material into the air or gas stream. Such pressurized vessels require periodic inspections, maintenance and testing to preclude deterioration and rupture that could pose a significant safety hazard. Pressurized vessels that contain rocks are potentially unsafe and are therefore typically fabricated with heavy-walled, welded steel.
Furthermore, with such pressurized vessels, when that vessel has been filled (charged) with rocks and abrasive particulate matter, and is thereafter pressurized, it is not possible to add more rock or material to the pressurized hopper without de-energizing the feed system altogether, thus slowing down the system operation.
In addition, such conventional abrasive blasting systems utilize an axial-feed screw for dispensing abrasive particulate material from the pressurized hopper into the air or gas stream. While the use of such systems provides a steady controlled rate of insertion of abrasive particulate, the operator cannot visually observe the process. As such, operators of such systems cannot visually perceive problems such as hang-ups or jamming of the abrasive media. The operator must either rely on experience or other sensory cues, or de-energize the system to investigate a feed problem.
It would, therefore, be advantageous to have an improved system and method for dispensing abrasive particulate material into a stream of air or gas that utilizes a hopper (containing the abrasive particulate material) that is open to the atmosphere (unpressurized), whereupon an operator can readily add more abrasive particulate material into the air or gas stream as required or needed, without the need to de-energize the system or shut down, thus increasing the efficiency and speed of the system in accomplishing the task.
It would be further advantageous to have an improved system and method for dispensing abrasive particulate material into a stream of air or gas that provides no pressure blow back, by virtue of using a hopper that is open to the atmosphere, and which is easily portable, lighter in weight, and safer than current pressurized screw feed system configurations.
It would also be further advantageous to have an improved system and method for dispensing abrasive particulate material into a stream of air or gas that utilizes a valve body and a sliding gate (two controls) to keep variable control of the introduction of abrasive particulate material into the hopper, rather than a feed screw, thus giving an operator better control of the dosing rate into the hopper, both mechanically and visually, and thus better control of the pipe cleaning and preparation process.
Accordingly, there is a need for an improved system and method of delivery of abrasive material into a gas stream for the purpose of cleaning, preparing and coating or lining the interior surface of in-service, small-diameter pipes. There is a further need for a pipe cleaning system which is operably able to introduce abrasive from a vessel under atmospheric conditions, rather than a pressurized vessel, whereby these abrasive materials can be introduced into a pressurized gas stream in a measured, highly-controlled and safe manner. To this end, the present invention effectively addresses these needs.